1. Field of the Invention
This invention relates to a rapidly curable method suitable for reaction injection molding for producing a polyurethane type composite which is excellent in high rigidity impact resistance and heat resistance.
2. Related Background Art
In the fiber reinforced plastics (FRP) molding technique of the prior art, the method of obtaining FRP by injecting a thermosetting resin such as unsaturated polyester resin, vinyl ester resin, epoxy resin, etc. into a mold in which a fibrous reinforcing material is previously set is generally called resin injection method or resin transfer molding method, and is known as the method with good economical efficiency utilizing in-mold polymerization.
In the field of industry, particularly the field of automotive industry, it has been demanded to manufacture construction materials having heat resistance in short molding cycle time. However, in the above methods, no satisfaction in both aspects of rapid curability and heat resistance has been obtained.
On the other hand, in the field of polyurethane elastomer, the reaction injection molding (hereinafter called RIM) technique has been developed and applied particularly to molding of bumper, facia etc. of automobile. Since this technique is suitable for manufacturing large size molding, specific features reside in that integration of a large number of parts is possible, and also that the molding cycle time is by far shorter as compared with the above resin injection method.
In recent years, it has been attempted to obtain a composite of thermosetting resin by means of rapid curing by combining the RIM technique with the resin injection method.
More specifically, it is a method in which a fibrous reinforcing material is previously set in a mold, and a thermosetting resin reaction liquid is injected by a RIM machine into the mold.
However, in the case of polyurethane type components used for RIM in the prior art, excessive increasing in viscosity occurs simultaneously with mixing, whereby penetrability into the fibrous reinforcing material is inferior, or even injection may be sometimes difficult. Also, there has been the drawback that no sufficient rigidity as the construction material can be obtained in the polyurethane of the prior art.
The polyurethane type components to be used for RIM molding of the prior art are susceptible to excessive increasing in viscosity simultaneously with mixing during preparation, and therefore it is inferior in penetrability into fibrous reinforcing material, even with injection being sometimes difficult, and its cured product has not attained sufficient rigidity as the construction material.